Vari-Mu Compression for Creative Distortion and Whatnot

So! Here's a new thing that I've been playing with the idea of. My dad gave me a bunch of tubes including a few remote-cutoff pentodes. I've been studying a lot of vintage schematics and come up with some ideas I'd like to try. Here's the first and simplest, primarily targeted to make interesting distortion sounds. Who knows if it'll work! I might add a feed-forward option. I have a bunch of ideas for these, but I'm not going to be able to get the parts for a while (saving up for a different toy) so in the meantime I'll be posting schematics as I manage to get them down.

Adventures in Reconing

Okay, I don't really recommend doing this. I have to point out though that the posts by J M Fahey on MEF and TGP were invaluable to the process.

My Twin came with a pair of Fender-labeled Utah speakers with torn (and moldy) cones. That sort of thing tends to happen when you ship a "135W" amp with a pair of 50W speakers, and then store it in a basement that's swamp-adjacent for thirty years.

Anyway, they were useless, so I got the bright idea that I could try reconing them and if it worked I'd have useful speakers, and if it didn't, I'd only be out $50.

Getting to this point was the hardest part.

So I cut the cone and surround out of the frame, measure them, and go looking for parts. I decided to go with the parts sold by Weber, as this was a guitar speaker and they sold guitar speaker parts. There are a couple other vendors, but not many as there's some weird shadowy cabal of speaker reconers and unless you get into it and start a business the vendors won't sell to you. It's basically crazy.

I decided to go nuts and order Kurt Meuller cones, in essence making the end result similar to Weber's 12F150B. The spiders Weber sells are cup-type while the original was flat, but this didn't turn out to matter too much. 

Alright, so cleaning the old gunk off of the basket was a huge pain. I used a heat gun, razor blades, I tried a couple solvents.. eventually I got it all off. Then it was just a matter of cleaning the voice coil gap, shimming the voice coil in the gap so that the coil is centered on the top plate, put the spider over the voice coil, and put the cone over that. Boom, first dry fit. 

This is actually after gluing, but you get the idea.

Now, ideally - and if you're using the correct parts - the spider and the throat of the cone will meet perfectly, so you can attach them both to the voice coil with one bead of adhesive. If you're a jerk like me and buy the wrong parts, they need a little massaging. In this case, I had to cut back the throat of the cone a fair amount, but I got it wrong from both sides - the spider was too tall and the cone was too deep. 

On the first speaker I reconed, I didn't do quite a good enough job of this and as a result the spider is pushed in at rest - not great for efficiency nor longevity. 

Also it's upside-down, which makes it hard to hear.

I did a lot of research - well, "research" - before starting this. Like I said at the top, J M Fahey was a huge help. There were a bunch of other people with opinions, but they tended to lead me astray. Like the people who suggested gel super glue for bonding voice coil/cone/spider - this worked very poorly for me. Also it left a mess when I used it to attach the dust cap.

Epoxy works much better. Contact cement was used to attach the spider, cone, and gasket to the basket. Solder the voice coil leads to the tinsel wire, solder the tinsel wire to the terminals, and boom, done. 

The second one came out nicer.

Now here's where the real craziness sets in - what to dope the surround with? There are two kinds of dope I've seen on guitar speakers: the clear stuff and the black stuff. The black stuff seems similar to what's used to seal cloth surrounds and I'm pretty sure that's just butyl rubber in a solvent. The best and cheapest candidate I've found to try is actually windshield adhesive. I haven't bought any, because I found a good DIY alternative for the clear stuff. 

Unlike a cloth surround where doping is necessary to block airflow, doping on paper surrounds is done to prevent cone cry and overall tame the breakup modes of the cone itself. If applied lightly it can contribute to that notch at 1.5kHz, and if applied heavily it can neutralize that notch at the expense of overall sensitivity. And you can look at what Celestion's done or what Jensen's done over the years, but I don't have the test equipment to optimize this process and I'm sure there are books somewhere about it.

In any case you want the doping compound to penetrate the paper and stay flexible. Some DIYers use rubber cement (thinned even) or white glue (PVA) but supposedly these don't stay flexible enough. After a bunch of research I found an adhesive known as EVA (ethylene vinyl acetate, as opposed to polyvinyl acetate). It's like regular white glue, but the addition of ethylene means it retains much more flexibility. You've seen EVA in at least one form - hot glue sticks. Finding an easy source of an EVA emulsion glue was a little trickier, but eventually I stumbled on Helmar Super-Tac.

Here's a blob of Helmar Super-Tac that I dried so I could play with it.

This blob here actually dried to a silicone-like rubberiness. It's pretty awesome stuff. Really thick like this, the surface dries much faster than the center so the water can't escape. Yes, that's right, it's water-based, which is a huge boon for DIY'ing. Also new applications of the glue (or water) dissolve the dried glue, which is great if you're applying multiple layers. Maybe not so great for ship building. 

I ran a few experiments with dilution ratios and I eventually used a 2:1 dilution of water:Super-Tac and applied about 6 coats to the surround of each speaker. 1:1 would've probably worked just as well. A straight application right out of the bottle might work too, but one coat is probably enough. I also found it was better to let the coats dry 8-24 hours before applying the next one. I rushed the second speaker and applied a couple coats within 4 hours of each other. It looked dry, but it wound up trapping a little extra water for a milkier look. This eventually wormed its way out though.

This is in the Peavey cab that I just stained.

Anyway, this resulted in what I'd guess is a light-to-moderate level of doping. I doped the first speaker and compared it to the undoped second side-by-side. And yep, a hair less sensitive but more tamed treble and a little more in the midrange. Once I liked it, I doped the second speaker to match, and they're now resting comfortably in a Randall 412 with a pair of Eminence OEMs from the 90s. 

I've left a whole lot out because I'm sick of typing. I ran a bunch of experiments on doping using the old cone material from the Utahs, though it turns out the cones I got from Weber are way more absorbent. Liquid latex never really soaked into the Utah, but maybe the Kurt Meuller cone would be different...

Super long story really short: for DIY doping of paper surrounds, try an EVA emulsion glue like Helmar Super-Tac.

Peavey Cab Refurb

So! I've been neglecting my blog for the past few months. I've been busy though. I imagine I'd keep this more current if the posting process weren't such an immense pain.

Anyway, I picked up this old Peavey combo cabinet (used to be a Stereo Chorus) on the cheap, and it'd already been mostly converted to a combo. The tolex had already been stripped and a new back panel added. Really about all I've done to this is sand it, stain it blue, and slap a few coats of shellac on it.

Shellac is probably a terrible finish for a speaker cabinet, but this cab is already beat to hell so I'm not really worried about it getting scratched/dented. Plus I had the shellac already, as well as the blue stain.

I mean, I didn't even make the grille, though I would like to do more work on it. Still have to add a jack plate. I guess this is kind of a silly post, but I just wanted to document that I did it.

Projects on deck

Just a quick inventory of what's popping around in my head. Decidedly incomplete. Maybe I'll start posting these every month. I don't post much on the blog because things move slowly, but hopefully I'll start posting more of the theory/planning end instead of just the rare instances when progress actually occurs.

In progress

• Peavey Windsor -> Matamp-y beast
• Kustom Defender 5H -> Bass preamp
• Portastudio -> live looper

Planning

• Repair mandolin neck joint
• Tube mic preamp(s) - redd47 redesign; design(s) from scratch
• Refurb/rebuild Stromberg-Carlson AU-36B
• Diode bridge compressor - trace V8 compressor in a pedal
• Vari-mu compressor
• parallel effects mixer pedal
• active variable crossover, xformer couple for splitting to guitar, bass amps
• "Phase Wizard"-y multi-amp buffered xformer isolated splitter
• Bogen CHB35A redesign
• Faceplates for rat rocket
• Geezer 212 bass cab rebuild
• gigantic 212 guitar cab overhaul
• mid-range driver box with 4, 8 ohm crossovers for bass cabs
• joystick noisemaker re-bulb, re-cap(?)
• 5 string j bass bridge pickup rout, replace
• 4 string p bass pickup replacement
• bari replacement neck on tele
• Randall 412 guitar cab load

Finished

• Nothing, ever.

Peavey Windsor mods

What a fun little toy.
Okay, picked this guy up cheap and I'm going to somewhat follow through on my "Matange" plans, except I'm dropping the Orange part in favor of a Matamp/JCM800 blend. Hey, its got a third preamp tube, why not?
So far all I've done cosmetically is move the back grille to the front. Not sure I'll do much more; maybe cut a new back grille out of expanded metal.
The preamp is currently fairly awful. Way too much gain, too little decoupling, lousy tone stack. I'm probably going to turn that cold clipper preamp stage into a cathode follower and the tone stack into a James with mid shift. I'll probably use the worthless "texture" control for the FAC. Then I'll use the "boost" relay to switch the second gain stage in and out.
For now I've started in on the power amp mods: 100k for the EL34 grid leaks, suppressors tied to cathodes, grid stoppers up to 47k, and 1k8 screen stoppers (didn't have any 1k5). Very noticeable improvement already!
Incidentally, Peavey seems to have paid the extra nickel for halfway-decent circuit board material. Id rather remove every component in this amp twice than remove one resistor on a Marshall made in the past decade.

5W Head to Preamp

I've been wondering what to do with this Kustom Defender 5H that was my introduction to tube amp building, as I don't really have much use for it lately. Somehow the idea popped into my head to use it as a bass preamp.

At first I tried the Garnet Herzog method - use the existing OT, hook up a dummy resistor, and tap the voltage off of it for the line out. It works okay, but the bandwidth is restricted/shaped on the OT. Not terribly useful for bass, as the stock Kustom OT is weak sauce. This worked fairly well for guitar though, and was simple.

Then I considered wiring up the EL84 as a cathode follower, but the required heater elevation and loss of a gain stage steered me away from that. If I had a couple more tubes, it might be worth it.

Eventually I settled on this:

The real key here is that Triad line matching transformer. It boasts 20Hz-20kHz response and only costs $6. I used a 5k pot to keep the output impedance low, and so I could balance the dropping resistor. The EL84, like any pentode, has an insane ra so the Zo is dominated by the Ra, in this case 2k5. The 220k resistor ensures that the pentode isn't excessively loaded and lowers the output voltage to something more reasonable for whatever power amp this gets connected to. After a pair of 12AX7 gain stages and an EL84, the output voltage could feasibly have been in the 200VAC range.

Oh yeah, and the load and cathode biasing resistor were picked off the load line. My Kustom is running around 350V B+ so I just roughly plotted the steepest line I could without nudging the max dissipation curve and guesstimated the plate and screen currents to pick a cathode resistor. It idles around 9W but clipping is symmetrical so there's no particular benefit to biasing it any warmer. Wattages could've been picked more carefully, but components were grabbed out of the parts bins.

Rk is bypassed; wish I hadn't missed that.

Capacitors are obviously non-ideal too, but this is just to publish the general idea.

As a bass preamp it sounds good, but it still needs a lot of tweaking and voicing before I'll post the schematic. The Triad transformer is good to its word and passes even a 5-string bass without attenuation. Plenty of bass and none of the shrill treble typical post-power amp line outs suffer from.

Also the Triad transformer can be wired for balanced operation, of course. The only other note I have is that this transformer is incredibly sensitive to radiated fields, so keep it away from the PT.

Clips and full schematic once I've got it really dialed in. I've got a Matamp-style preamp in there now and it's nice and versatile but not fantastic with heavy overdrive. Probably understandable considering there are only three gain stages.

I'll probably wind up dropping the screen voltage, but the headroom is so low on the EL84 already. Hmm.

Adventures in PL Premium

So, I have the bulk of the gluing done. I have a bead around all the inside edges, and I've glued in all the primary braces. There are four front-to-back, two side-to-side, and two top-to-back. The top panel is going to be partially braced by the shelf port assembly.
Hopefully this amount of bracing will be sufficient to prevent resonating panels. We'll find out after the glue cures, and I wouldn't be surprised to find I need a couple more on the bottom, top, and shelf panels.
PL Premium is the go-to adhesive for speaker cabinets, as it expands while it cures to form air tight seals. It is fairly nasty stuff though; the tube says it's okay for indoor use, but the offgassing is fairly odorous so I can't imagine it being used in anything besides original construction. All the braces are screwed also, so as long add it does a reasonable job, this thing'll be rock solid.

WinISD Plots of My Bass Cab Projects

So! Here are some of the plots I've been making decisions with. The yellow plots are the Eden Nemesis 212 with the MCM 55-2982 drivers, and the white plots are the Peavey TNT130 that I'm converting into a cab with the Dayton Audio PA380-8 (Parts Express's house brand). 

First, expected SPL:

SPL from my amp

The white trace is lower since, as an 8 ohm cab, it's only going to get ~125W from my amp, while the 4 ohm 212 gets the full 250W. That peak around 80 Hz makes the 212 sound really fat, and somewhat boomy, though I'm hoping that adding bracing will reduce that somewhat.

Maximum Power

Power ratings of speakers in bass cabs are largely useless; most speakers are excursion-limited rather than thermally limited. You can increase the safe power handling by raising the port tuning, though that comes with tonal consequences. I did that somewhat already with the TNT cab, but 50Hz is a pretty common cab tuning in commercial cabs. I'm guessing this is partially why. As you can see on the SPL graph, it doesn't hurt the low end (only down 3dB by 50Hz).

Cone Excursion. Yellow = 7mm Xmax, White = 5mm Xmax

Also on the "safety" front (or just designing speakers that don't explode from regular use), here's a plot of the cones excursions at various frequencies. The MCM drivers have a specified Xmax of 7mm, which is huge (probably meant to be a subwoofer) and the Dayton has an Xmax of 5mm (not showing up on the graph for some reason.)

Clearly neither speaker is going to take much (any) 30-40Hz content, so a high-pass filter is a good idea. Fortunately the Trace Elliot head I have does have the ability to remove these two bands. I might still add one to deal with any extraneous subsonic noise that gets through.

Port Velocities. Good enough, Eden.

 And the last plot is of the port velocities per frequency. There are various rules of thumb to avoid port chuffing, but the one I was following was 19 meters per second. Eden does fine with the single 6" port, and my gigantic shelf clearly is going to be fine.

So yeah, I like music enough to get into math, physics, and now woodwork. Good times. 

Peavey cab bracing

Busy day! I got 2 of the 3 dimensions braced, and got the cutout for the jack cup done.
The braces are going to be screwed and glued. I cut little Xs in the tolex before I drilled pilot holes, and I'm going to counter-sink the screws a bit so I cab glue the tolex back over the screw head. It won't be seamless, but it'll look better than screw heads sticking out.
Still trying to figure out how I want to mount the shelf port, and I cut the back panel 1/16" too tall, so I'll shave that down.
Gluing day is going to be a real treat; I've got to place the braces in a certain order or they block each other from fitting, and some of them are so tight they have to be hammered into place. Fortunately there's some working time with PL premium.
Can't wait to hear this thing!

Peavey cab update

I got the big panels taken out of the divider (why did they use OSB for the baffle and back but ply for the divider?!) and "Swiss cheesed" the material I couldn't rout out.
I don't think I'll drill holes through the other braces unless I get really bored. To be clear, this does have a purpose: not only am I removing weight from the cab, but I'm also increasing the volume of air available inside the cabinet. The front-to-back internal dimension is actually only 9 5/16", so without any bracing or the speaker I only have a maximum of 2.9 cu. ft. to work with. Cutting big holes is obviously great, but cutting 3/8" jokes in 3/4" square braces? Probably not so much.
Also, not going to lie, six year old me was really happy doing this.
I have most of the braces cut already, so the next step is screwing and gluing them in place. Not really looking forward to trying to tune the shelf port. It's so big that the length calculations are fairly insensitive to minor variations, so hopefully it won't be too bad.

Peavey Bass Cab Conversion

This is a Peavey tnt Combo, a bass combo amp that put out 50W. The amp part is long gone, but I got the cab for a whopping $15. It has separate chambers for the amp and the "ported" speaker enclosure.

The existing speaker enclosure part is only about 1.8 cu. ft. thanks in part to the shallow construction (10" internally, front-to-back) but also to the section reserved for the amp (4" of height!). The overall maximum internal volume is roughly 3 cu. ft., which is a great starting point. I'm going to brace the hell out of this cab and use the existing front slot for a shelf port. I'm assuming/hoping for roughly 2.5 cu. ft. after installing the speaker, all the bracing, the volume taken up by the port.

The baffle is actually OSB (chipboard) so it might make sense to just replace it, but I'm going to try to avoid that for now. It's dadoed into place, but actually rattling so hopefully a bead of adhesive and possibly some cleats will fix that.

I've been having fun in WinISD trying to find a decent (and cheap) driver for this box. I've finally settled on the Dayton Audio PA380-8, which is (thermally) rated to 500W. I'm going to tune the cab to 50 Hz, which looks life an optimal point for balancing low-end extension and excursion. I'll add the plots from WinISD when I get a chance.

50 Hz is on the high end of bass guitar cab tuning, but a lot of commercial cabs are actually tuned about here. While a low E string is around 40Hz (and the B below that roughly 30Hz), not much of that fundamental is picked up by, well, the pickups. By far, the more important frequency to worry about is the second harmonic (first octave), which will be 80 (or 60) Hz. If you'd like to see evidence of this, search the TalkBass forums for "waterfall plots", which show frequency spectrum content over time in a lovely 3D format.

Anyway, even with the cab tuned to 50 Hz, the driver I've chosen hits -3dB around 50Hz, so even the low B should be quite loud. As much as I wish I were making a subwoofer, I'm not, so I don't need to worry about covering that range.

Plus my other bass cab is tuned to 45 Hz. That one's a real treat, an Eden Nemesis 212 that I fitted with MCM drivers. That cab requires a great deal of bracing as it can shake roughly 100 pounds of other amps and cabs to the floor. Not that I've let it, but objects that size and mass being turned into that old electronic vibrating football game, well, that's just a massive waste of energy.

But back to this Peavey: I've got to seal the back where the amp used to be, cut out the internal "top" that separated the amp from the cab, brace the living daylights out of it, verify the tuning, and then line the inside.

Total cost so far:
Cab- $15
Baltic birch- $35
Driver- $75
Jackplate- $5

Still need to buy: adhesive, lining, screws, paint, etc.

How it starts...

Nothing to it.

These are some quick plans for a portable record player I picked up a while back. It's got a pair of 50C5 tubes for about 5W in push-pull, one 12AX7, and a hot chassis.

I'm going to add a second preamp tube and an isolation transformer, and use the extra gain stage for bias-mod tremolo. I ripped that shamelessly from Fender; might add NFB too, make it a tiny Princeton.

You'll probably notice I write ohm's law and the equation for finding knee frequencies over and over again. I blame chemistry. It's not a bad habit, but it does look silly looking back at your notes.

Hopefully this posts; I apparently can't comment on my own posts or format things the way I want on my phone or computer, but I blog so infrequently that it's probably not worth migrating to a new blog host. So, sorry! I'm not ignoring you!

I'm surprised it's let me type this long; I shouldn't push it any further...

More Rockette Tweaks

Finally got around to putting the bright cap on a switch. Also added a 500pF cap option. Eh, you got some center-off DPDT switches lying around, you stay using 'em.

It's okay, nothing to write home about.

I'm also planning on making the bridged channels selectable. Using both sides of the LTP wins up costing you some gain, and why not get that back?

Also, I might as well add a sag resistor, put that on a switch too. I'm pretty proud of how rock-sold the power supply is, and the modest plate voltage, but

So a total of three switches that are pretty superfluous.

I don't know; what the hell. It's my amp.

Trace Elliot Love

I scooped up this Trace Elliot AH500X about a month ago. It is... Fantastic. It was the top of the Trace line back in the 80s, and it boasts a pair of 250W into 4 ohm power amps, for a bowel-shaking 500W at 2 ohms.
There's talk of "Trace watts" because these seem louder than similarly-rated amps, but perhaps the better description is "honest watts" as from what I've read, they do spec as advertised. Maybe it's just that they require you to use more cabs to get the full power output.
Starting at the beginning: active and passive inputs. Sure. The preamp gain control has three lights: a yellow "OK" light in the center, a green arrow telling you to turn up, and a red arrow warning you of clipping. Really nice touch.
Then it's got a 12-band graphic EQ, which is defeatable. Very nice to have 30 and 40 Hz to cut. It also has an EQ preset, which gives a nice mid scoop sound. Both of these are foot switchable, and while a mid scoop isn't the best idea for a regular tone, I can see it being useful for occasional accents. There's also a defeatable noise gate which I haven't really tested thoroughly but is certainly unintrusive.
Then there's an effects loop, a transformer-isolated DI out, and a master volume. As they mention in the owner's manual, Trace Elliot expects the user to set the preamp for maximum gain and use the master for overall volume level.
In addition to the effects loop, there's an additional (parallel) power amp in and out.

The back panel is where things get nuts.


So two power amps, each has its own volume control. It seems silly, having volume controls after the master, but it's actually very useful.
Each power amp also has a line level effects loop, which can, of course, also be used as line out and line in. The power amps also can be configured for dual mono, stereo, or biamping with a crossover that's adjustable from 250
Hz to 1 kHz.
Which is pretty crazy as far as versatility goes.


Plus there's a freaking blacklight!
It weighs in the ballpark of 60 pounds, apparently 30 of those pounds are 25 years of dust, and I really wish
I could've afforded those 1818X cabs.

I'm still learning how to tweak this thing, but biamping with the highs sent to a guitar cab is fantastic. I've also been researching bass cab design, which is another whole ball of wax, albeit fascinating.
If my winisd skills are any good at all,
I'll be posting about a couple cabs
I'm fitting with mcm drivers, bracing, and
(re)dampening.

I may even have to put the Matange project on hold, in favor of more live gear.
Still flipping the coin on that one.

The Matamp NFB circuit

Oh good, my phone lost my blog post.

Well, there's an LC notch filter in the Matamp's NFB loop, which seems clever except for inductors' sensitivity to noise, adding phase shifts in a marginally stable NFB loop (that anode bypass cap isn't an accident, nor is the speed up cap parallel to the feedback resistor) - plus we have an extra stage in the loop thanks to the cathodyne.

Also I should point out that when you inject NFB into the driver before a cathodyne, any presence/resonance controls serve to partially bypass the driver's cathode for a double dose of whatever range you're trying to boost. The blackface Princeton gets around this by fully bypassing the cathode and then applying NFB between the regular Rk//Ck and ground.

So the Matamp idea is an interesting one, but it's clear why it didn't last. I prefer building stable amps to GHz oscillators, plus shielded inductors are expensive, so I'll probably not bother with implementing this. Maybe an overall NFB control. Maybe.

You know what's easier to keep stable, and lets you implement a notch filter with adjustable frequency and Q? A local feedback loop.

It's not a horribly unique idea - check out the Electro-Harmonix Tube Zipper sometime. There's also a German patent on a similar circuit. As far as active mid boosts go, though, it could be super interesting. Either you could add a gentle Matamp/Orange mid boost, or sharpen the Q and get a "cocked wah" sound, or even defeat the loop for a gain boost... If you wanted to get really clever, you could even sweep the frequency at a constant Q, but at that point just buy a Tube Zipper. Puretube (who also designed the Flanger Hoax) is one of my heroes. Give him monies.

I'll fiddle with this idea first using a Kustom Defender 5H, turning it into basically a massive pedal. It might be a huge waste of time, who knows. Plus the James stack is perfectly capable of creating a "mid boost" by itself...

But seriously, puretube is a brilliant fellow.

The Matange!

So, I've been planning my next project lately. This year, I'm going to build an Orange/Matamp-inspired head, starting with a cheap donor. Still not going to make the plunge into woodwork/metalwork as long as I can avoid it. Someday I might build a high-gain monstrosity, but I'm not a big fan of preamp distortion, so I don't have much motivation.
Fortunately, I have the relevant schematics on my phone!
Now, my thoughts:
Fixed bias quad of pentodes. Sure, though it pains me to turn away from my beloved beam tetrodes, but I'll give these screen-current-sucking babies a try.
Cathodyne phase inverter. Awesome; love it. It's going to need a big grid stopper, and I'll put big grid stoppers on the power tubes too. Definitely going with AC coupling; DC coupling is too big of a pain for little benefit with cathodynes. What can I say, I like em center-biased.
James tone stack. Absolutely. I'll probably add, or at least try, a mid shift control so I can move the notch around.
The "FAC" switchable coupling cap bass control. This is great; I've used it for a bass control after a pentode. The series-connected version does pop; Matchless uses a parallel "one at a time" version with large resistors in parallel to prevent this. Since I've tried the series version, I'll probably try Matchless's take on the Matamp original.
The Matamp drive control. This kind of seems silly. Switchable bright cap, eh, why not. Gotta keep some British in there! I don't see the point in padding down the gain when there are only three gain stages. Also that Orange inductor-based boost control... I'm skeptical. I'm also worried about noise. It's a tricky situation. I might try variable cathode bypassing instead, possibly tied to a treble cut.
As for the order of the tone controls, I think I prefer having the FAC after the first gain stage and the James after the second. Always good to cut bass early and treble late, though there are so few stages...
It should be an interesting project. If there's space for a third preamp tube, I may use a 6GH8 triode/pentode to add reverb. I'll use the pentode to drive the tank and half of a 12AX7 for the recovery stage, and then I can use that medium-mu triode in the 6GH8 for the phase inverter! Mmmmm, sweet, sweet low-ra cathodynes...
More when I actually write up a schematic.